1. UNIT 1: ATOMIC STRUCTURE & NUCLEAR CHEMISTRY HONORS Chemistry Grafton High School

2. UNIT OBJECTIVES: SWBAT:

3. Key Questions How did the concept of the atom change and develop from the time of Democritus to the time of John Dalton? What is the structure of the nuclear atom? What are the three kinds of subatomic particles? What makes one element different from another? How do isotopes of an element differ? How do you calculate the atomic mass of an element? How do nuclear reactions differ from chemical reactions? What are the three types of nuclear radiation? How much of a radioactive sample remains after each half life? What are three devices used to detect radiation? What are some practical uses of radioisotopes?

4. The ATOM An atom is the smallest particle of an element that retains its identity in a chemical reaction. Although early philosophers and scientists could not observe individual atoms, they were still able to propose ideas about the structure of atoms.

5. HELIUM ATOM + N N + - - proton electron neutron Shell What do these particles consist of? Helium Atom

6. Particle proton neutron electron Charge + ve charge -ve charge No charge 1 1 nil Mass Subatomic Particles

7. the number of protons in an atom the number of protons and neutrons in an atom He 2 4 Mass Number Atomic number number of electrons = number of protons Numbers on the Periodic Table

8. Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. first shella maximum of 2 electrons second shella maximum of 8 electrons third shella maximum of 8 electrons Energy Levels (shells)

9. With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example; N Nitrogen 7 14 2 in 1 st shell 5 in 2 nd shell configuration = 2, 5 2 + 5 = 7 Electron Configuration

10. Electron Configuration ~ Bohr Model Each orbital can hold a certain number of electrons. Orbitals (shells) fill from the inside (nearest nucleus) out.

11. EXAMPLES of electronic configuration for the following elements: Ca O ClSi Na 20 40 11 23 8 17 16 35 14 28 B 11 5 a)b)c) d)e)f) 2,8,8,22,8,1 2,8,72,8,42,3 2,6 Electron Configurations

12. With Bohr diagrams, elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example: Nitrogen N X X X X XX X N 7 14 Bohr Diagrams

13. Draw the Dot & Cross diagrams for the following elements; O ClCl 8 17 16 a)b) O X X X X X X X X Cl X X X XX X X X X X X X X X X X X X 35 Examples of Bohr Diagrams

14. Isotopes ~ varying # of neutrons Atoms of a certain element all have the same number of protons Number of neutrons may vary The different variations in # of neutrons for a certain element are called ISOTOPES Atomic Mass (decimal)= number of protons + average number of neutrons from all isotopes Isotopes of Carbon

15. Looking at isotopes The different numbers of neutrons in isotopes gives them different masses Isotopes of an element do not occur in equal amounts: Example:

16. Isotopic Abundance Isotopic Abundance = Percentage of an element’s atoms that exist as each isotope Each isotope has its own mass that is different from other isotopes of that element. Isotopic mass is the average mass of the atoms of a specific isotope of an element. Determines the isotope number

17. Relative Atomic Mass WATCH: https://goo.gl/4y80yzhttps://goo.gl/4y80yz What does the atomic mass on the periodic table measure? The relative atomic mass shown as a decimal on the periodic table is the amount of protons plus the weighted average number of isotopes for that element: Atomic Number Chemical Symbol Relative Atomic Mass

18. Calculating Relative Atomic Mass NOTE: Use the percent abundance of the isotopes as a DECIMAL Relative Atomic Mass (Average Weighted Mass): Relative Atomic Mass = (% Isotope A as decimal x Isotopic Mass Isotope A) + (% Isotope B as decimal x Isotopic Mass Isotope B) + (% Isotope C as decimal x Isotopic Mass Isotope C)

19. EXAMPLE: Calculation of Relative Atomic Mass for Carbon:

20. Atomic Mass Unit (AMU) The unit of measurement for an atom is an AMU AMU = Atomic Mass Unit ONE (1) AMU = mass of ONE (1) proton Why NOT grams?

21. Atomic Mass Unit (AMU) There are 6 X 10 23 or 600,000,000,000,000,0 00,000,000 amus in one gram (Remember that electrons are 2000 times smaller than one amu/one proton)

22. Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of ________ (1876-1934). One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of ________ (1876-1934). She discovered ________, the spontaneous disintegration of some elements into smaller pieces. She discovered ________, the spontaneous disintegration of some elements into smaller pieces. WATCH: https://goo.gl/IyuRj4 WATCH: https://goo.gl/IyuRj4https://goo.gl/IyuRj4

23. Nuclear Reactions vs. Normal Chemical Changes Radioisotopes are isotopes with unstable nuclei and undergo radioactive decay Radioisotopes are isotopes with unstable nuclei and undergo radioactive decay Nuclear reactions involve the nucleus Nuclear reactions involve the nucleus The nucleus opens, and protons and neutrons are rearranged The nucleus opens, and protons and neutrons are rearranged The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy “Normal” Chemical Reactions involve electrons, not protons and neutrons “Normal” Chemical Reactions involve electrons, not protons and neutrons

24. Mass Defect Nuclear reactions involve energy changes many times the magnitude of chemical changes Nuclear reactions involve energy changes many times the magnitude of chemical changes Chemical reactions – Energy is conserved Chemical reactions – Energy is conserved Nuclear reactions – Small loss of matter (mass defect) releases tremendous energy (some of the mass can be converted into energy Nuclear reactions – Small loss of matter (mass defect) releases tremendous energy (some of the mass can be converted into energy Shown by a very famous equation! Shown by a very famous equation! E=mc 2 EnergyMass Speed of light

25. Types of Radiation Alpha (ά) – a positively charged helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons Alpha (ά) – a positively charged helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons Beta (β) – an electronBeta (β) – an electron Gamma (γ) – pure energy; called a ray rather than a particleGamma (γ) – pure energy; called a ray rather than a particle

26. Other Nuclear Particles Neutron Neutron Positron – a positive electron Positron – a positive electron Proton – usually referred to as hydrogen-1Proton – usually referred to as hydrogen-1 Any other elemental isotopeAny other elemental isotope

27. Penetrating Ability

28. Balancing Nuclear Reactions In the reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation) Atomic numbers must balance and Mass numbers must balance Use a particle or isotope to fill in the missing protons and neutrons

29. Alpha, Beta, and Gamma Particles Atoms are not all stable. Excess energy in an unstable atom is released in a basic particle or wave Greek alphabet is used to name particles (in order of their discovery)

30. REMEMBER! The nuclear structure changes with radioactive decay, but radioisotopes are NOT chemically different!

31. Alpha Particles Heaviest particle Rays, NOT waves –made of high-energy particles that are expelled from unstable nuclei Alpha particle is a helium ion Not very penetrating; easily absorbed SPEED: 16,000km/sec (1/10 th speed of light!)

32. Nuclear Reactions Alpha emission Alpha emission Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2. Nucleons (nuclear particles… protons and neutrons) are rearranged but conserved

33. Beta Particles LIGHTER energy particles Energetic electron given off by unstable nuclei to restore energy balance Stopped by aluminum (few mm thick) or 3 meters of air 8,000 times smaller than alpha particle SPEED: 270,000 km/sec Can cause cellular damage

34. Nuclear Reactions Beta emission Beta emission Note that mass number (A) is unchanged and atomic number (Z) goes up by 1. This is because it is caused by a neutron that breaks apart into a proton and electron (electron is emitted).

35. Other Types of Nuclear Reactions Positron ( 0 +1  ): a positive electron Electron capture: Electron capture: the capture of an electron 207

36. Gamma Ray HIGH-ENERGY photon (light wave) Same family as X-rays and light MORE energetic and harmful Damaging to living cells Slows down energy by transferring it to cell components

37. Artificial Nuclear Reactions New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4 He and 11 B. Reactions using neutrons are called  reactions because a  ray is usually emitted. Radioisotopes used in medicine are often made by  reactions.

38. Artificial Nuclear Reactions Example of a  reaction is production of radioactive 31 P for use in studies of P uptake in the body. 31 15 P + 1 0 n ---> 32 15 P + 

39. Transuranium Elements Elements beyond 92 (transuranium) made starting with an  reaction 238 92 U + 1 0 n ---> 239 92 U +  239 92 U ---> 239 93 Np + 0 -1  239 93 Np ---> 239 94 Pu + 0 -1  239 93 Np ---> 239 94 Pu + 0 -1 

40. Nuclear Fission

41. Fission is the splitting of atoms Fission is the splitting of atoms Controlled reaction Controlled reaction These are usually very large, so that they are not as stable These are usually very large, so that they are not as stable Nuclear Power stations use heat released by nuclear reaction (nuclear fission) to boil water to make steam Nuclear Power stations use heat released by nuclear reaction (nuclear fission) to boil water to make steam

42. Fission Process - MODEL

43. Nuclear Fission & POWER Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. 17% of the world’s energy comes from nuclear. 17% of the world’s energy comes from nuclear.

44. Diagram of a nuclear power plant

45. Nuclear Explosion Explosion occurs when reaction is allowed to run out of control Large amounts of ENERGY released QUICKLY WATCH: Nuclear reactor controls rate of energy release Uranium oxide held in fuel rods Rods lowered into reactor core Coolant (CO2) circulated to remove heat Control rods in core absorb neutrons and control rate of chain reaction Raised to speed up; lowered to slow down

46. Nuclear Fusion Fusion small nuclei combine 2 H + 3 H 4 He + 1 n + 1 1 2 0 Occurs in the sun and other stars Energy

47. Nuclear Fusion Fusion Excessive heat can not be contained Attempts at “cold” fusion have FAILED. “Hot” fusion is difficult to contain

48. Half-Life HALF-LIFE is the time that it takes for 1/2 a sample to decompose. HALF-LIFE is the time that it takes for 1/2 a sample to decompose. The rate of a nuclear transformation depends only on the “reactant” concentration. The rate of a nuclear transformation depends only on the “reactant” concentration.

49. Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half- lives? After 5 half-lives?

50. Kinetics of Radioactive Decay For each duration (half-life), one half of the substance decomposes. For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234 After 3.6 days > 25 grams After 7.2 days > 12.5 grams After 10.8 days > 6.25 grams

51. Learning Check! The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours?

52. Effects of Radiation

53. Geiger Counter Used to detect radioactive substances

54. Radiocarbon Dating Radioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmic radiation 14 N + 1 o n ---> 14 C + 1 H The C-14 is oxidized to CO 2, which circulates through the biosphere. When a plant dies, the C-14 is not replenished. But the C-14 continues to decay with t 1/2 = 5730 years. Activity of a sample can be used to date the sample.

55. Nuclear Medicine: Imaging Thyroid imaging using Tc-99m

56. Food Irradiation Food can be irradiated with  rays from 60 Co or 137 Cs.Food can be irradiated with  rays from 60 Co or 137 Cs. Irradiated milk has a shelf life of 3 mo. without refrigeration.Irradiated milk has a shelf life of 3 mo. without refrigeration. USDA has approved irradiation of meats and eggs.USDA has approved irradiation of meats and eggs.